Apparatus and method for producing shear deformation

ABSTRACT

An apparatus for producing shear deformation in a work piece, the apparatus comprising: a processing channel through which the work piece passes, the processing channel including first and second channel sections which intersect at an angle to each other; a plurality of drive members configured to engage sides of the work piece to drive it through the processing channel so that the work piece passes from the first channel section to the second channel section to produce shear deformation in the work piece; and a drive surface disposed at an intersection of the first and second channel sections, the drive surface being configured to engage the work piece and advance it through the intersection, wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece to maintain drive of the work piece through the processing channel.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method of processing amaterial by performing a shear deformation process. More particularly,but not exclusively, the invention relates to producing sheardeformation in a metal.

BACKGROUND OF THE INVENTION

Severe plastic deformation processes can be used to improve the physicalproperties of a material. Machines for producing shear deformation in awork piece have been previously proposed though reduction to commercialpractice has been problematic. In particular, the process has beendifficult to maintain for continuous sheet products as the work piecehas a tendency to jam in the apparatus, causing the process to halt.

Examples of the invention seek to solve, or at least ameliorate, one ormore disadvantages of previous machines for producing shear deformationin a work piece.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an apparatus forproducing shear deformation in a work piece, the apparatus comprising: aprocessing channel through which the work piece passes, the processingchannel including first and second channel sections which intersect atan angle to each other; a plurality of drive members configured toengage sides of the work piece to drive it through the processingchannel so that the work piece passes from the first channel section tothe second channel section to produce shear deformation in the workpiece; and a drive surface disposed at an intersection of the first andsecond channel sections, the drive surface being configured to engagethe work piece and advance it through the intersection, wherein opposingsides of the first channel section are defined by a pair of die facesrelative to which the drive members are rotatably fixed, the separationof the die faces being variable in response to thickness variations ofthe work piece to maintain drive of the work piece through theprocessing channel.

According to the present invention, there is also provided an apparatusfor producing shear deformation in a work piece, the apparatuscomprising: a processing channel through which the work piece passes,the processing channel including first and second channel sections whichintersect at an angle to each other; a plurality of drive membersconfigured to engage sides of the work piece to drive it through theprocessing channel so that the work piece passes from the first channelsection to the second channel section to produce shear deformation inthe work piece; and a drive surface disposed at an intersection of thefirst and second channel sections, the drive surface being configured toengage the work piece and advance it through the intersection, whereinopposing sides of the first channel section are defined by a pair of diefaces relative to which the drive members are rotatably fixed, theseparation of the die faces being variable in response to thicknessvariations of the work piece so that the pressure imparted by the drivemembers on the work piece is maintained at a substantially constantlevel.

Preferably, each die face includes a plurality of drive members eachseparated by a guide plate to support the material and thus to preventbuckling. An external surface of the drive members can extend into thefirst channel section to impart pressure on the work piece. Preferably,each drive member is in the form of a roller, an external surface ofwhich forms part of the die face.

Preferably, the rollers of a respective die face are disposed within adie block, an outer surface of which forms the die face. The separationof the die faces can be varied by moving a single die block relative tothe other die block. The single die block can be slidably supported on aplurality of shafts which are disposed perpendicular to the firstchannel section so as to allow the separation of the die faces to vary.

Movement of the die block along the shafts can be restrained by theaction of a resilient spring element acting on the die block so that apressure imparted on the work piece by each die face remainssubstantially constant.

Preferably, at least one of the shafts has a head at one end thereof andthe resilient spring element is a plurality of spring washers which aredisposed between the at least one head and the die block.

The single die block can be movable under the action of a hydraulicsystem.

In one embodiment, the drive members include a plurality of opposingclamping elements.

Preferably, the clamping elements are disposed around a pair of endlessdrive members, the clamping elements engaging the work piece as theytravel around a straight portion of each endless drive member.Preferably, each endless drive member is a chain.

Preferably, a surface of the clamping elements which is arranged toengage the work piece is grooved, the grooves configured to acceptcorresponding protrusions on a support member so that as the clampingelements pass around a curved portion of an endless drive member,contact with the work piece passes from the clamping elements to arespective support member.

The support member can be fixed relative to the apparatus and an outerface of the support member can form a part of the first channel section.Preferably, the separation of the clamping elements is variable underthe action of a hydraulic system.

Preferably, the apparatus further includes a plurality of drive membersdisposed in the second channel section to pull the work piece throughthe processing channel. Preferably, the drive members are configured sothat a combined contact area of the drive members acting on the workpiece in the first channel section is substantially equal to a combinedcontact area of the drive members acting on the work piece in the secondchannel section.

The apparatus can further include a roller at the intersection of thefirst and second channel sections, the roller being disposed across theprocessing channel from the drive surface. Preferably, the radius of theroller is less than half the thickness of the work piece to obviate areduction in the shear deformation of the work piece. In practice, thedrive surface is at the outer side of the corner formed by theintersection and the roller is at the inner side of the corner.

Preferably, the apparatus further includes a lubrication systemconfigured to apply lubricant to the work piece before the work piecepasses through the intersection.

Preferably, the drive surface is an external surface of a roller.

According to the present invention, there is also provided a method forprocessing metals, including driving a work piece to be treated througha processing channel, the processing channel having first and secondchannel sections which intersect and are disposed at an angle to eachother, the work piece undergoing shear deformation at the region ofintersection between said first and second channels, wherein the workpiece is driven through the first channel section by engagement of thework piece with a plurality of drive members, the method includingvarying a separation of the drive members in response to thicknessvariations of the work piece to maintain drive of the work piece.

Preferably, the work piece is driven through an angle of approximately90 degrees when passing through the intersection. Preferably, the drivemembers engage the work piece in both the first and second channelsections and the contact area of engagement in the first channel sectionis substantially equal to the contact area of engagement in the secondchannel section.

The method can further include the steps of twisting a leading edge ofthe work piece after it exits the second channel, fixing it to atrailing edge of the work piece to form a continuous mobius strip andfeeding it back into the first channel. Preferably, the mobius strip ispassed through the processing channel four times.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described, by way of non-limiting exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a schematic sectional diagram of an apparatus for producingshear deformation in a work piece of one embodiment of the invention;

FIG. 2 is close sectional view of the apparatus of FIG. 1;

FIG. 3 is another close sectional view of the apparatus of FIG. 1, thesection taken along a different plane;

FIG. 4 is a close schematic diagram of another apparatus for producingshear deformation in a work piece;

FIG. 5 is a perspective view of another apparatus for producing sheardeformation in a work piece;

FIG. 6 is a close side view of the apparatus of FIG. 5;

FIG. 7 is a closer view of the apparatus of FIG. 5;

FIG. 8 is a close perspective of the apparatus of FIG. 5; and

FIG. 9 is another close perspective of the apparatus of FIG. 5 with oneof the support members removed for clarity.

DETAILED DESCRIPTION

With reference to FIG. 1, there is shown an apparatus 10 for producingshear deformation in a work piece. The apparatus 10 comprises aprocessing channel 12 through which the work piece passes. Theprocessing channel 12 includes first and second channel sections 14, 16respectively which are of substantially equal cross section andintersect at an angle to each other. The first and second channelsections 14, 16 are shown as being at an angle of 90 degrees to eachother, though it will be appreciated that the first and second channelsections 14, 16 could be arranged at other angles which would preferablybe in the range of 90 to 135 degrees.

A plurality of drive members 18, in the form of opposing drive rollers,are provided and are configured to engage sides of the work piece todrive it through the processing channel 12 so that the work piece passesfrom the first channel section 14 to the second channel section 16 toproduce shear deformation in the work piece.

The apparatus 10 also comprises a drive surface 20, in the form of anexternal surface of a drive roller, which is disposed at an intersectionof the first and second channel sections 14, 16 at the outer side of thecorner formed by the insection. The drive surface 20 is configured toengage the work piece and advance it through the intersection. Areplaceable wear tip 31 may be disposed across from the drive roller 20at the inner side of the corner formed by the intersection. The wear tipmay be formed of tungsten carbide.

As illustrated in FIG. 2, opposing sides of the first channel section 14are defined by a pair of die faces 22 a, 22 b, relative to which thedrive rollers 18 are rotatably fixed. The separation of the die faces 22a, 22 b is variable in response to thickness variations of the workpiece to maintain drive of the work piece through the processingchannel. Variation of the separation of the die faces 22 a, 22 b allowsthe pressure imparted by the drive rollers 18 on the work piece to bemaintained at a substantially constant level.

It was not previously considered that variations in the gauge of thematerial used for a work piece had any substantial affect on theprocess. Having regard to the magnitude of the thickness variations incomparison to the forces required to produce shear deformation, such anissue has previously been considered counterintuitive because thevariation in material thickness is generally small, in the order oftenths of a millimetre, and materials typically used in the sheardeformation process have elastic properties which allow them towithstand increased contact pressures. Surprisingly, it has been foundthat variations in the thickness of a work piece, even variations withinmanufacturer's tolerances, can lead to interruptions in drive of thework piece and bring the process to a halt.

The applicant has found that by providing an apparatus which can takeinto consideration slight variations in material thickness and provide aconstant driving pressure on the work piece, drive may be maintained onthe work piece and unintentional interruption of the process can bereduced, thereby allowing for a more continuous process to be achieved.

In prior apparatus, the height of the first channel 16 or the gapbetween the die faces 22 a, 22 b or the drive means 18, which typicallyincludes rollers or a belt, was equal to the nominal thickness of thegauge of the incoming material. In practice, the thickness of the workpiece would vary a small amount and, as a result, when the work piece isfed through the fixed-gap rollers, the rollers will apply less or morepressure on the work piece as the thickness decreases and increasesrespectively. When a thicker section of work piece passes through therollers, the material may be plastically deformed, which in turnwork-hardens the material before it goes through the shear process. Notonly will this affect the outcome of the process, but it can alsoextrude the material and cause damage to the equipment. When thinnermaterial passes into the rollers, the rollers can lose traction whichaffects their ability to drive the work piece through the machine,causing the process to stall.

In one example, each die face 22 a, 22 b includes a plurality of driverollers 18 each separated by a guide surface 24 which supports thematerial and prevents buckling. The surface 24 may be in the form of aplate. An external surface of the drive rollers 18 extends into thefirst channel section 14 to form part of the die face and to impartpressure on the work piece to engage it and drive it through theprocessing channel 12. As the drive roller extends into the firstchannel section, compressive forces will be imparted onto the workpiece. The level of compressive stresses in the work piece will be belowa level at which plastic deformation occurs so that the work piece isnot extruded as it passes through the processing channel 12.

The drive rollers 18 of a respective die face 22 a, 22 b are disposedwithin a respective die block 26 a, 26 b. An outer surface of each dieblock 26 a, 26 b incorporates the buckling surface 24 so that the outersurface forms the die face 22 a, 22 b.

By incorporating the drive rollers 18 and the guide surface 24 into adie block, the separation of the die faces 22 a, 22 b can be varied bymoving either or both of the die blocks. For simplicity, in apparatus10, only a single die block, the inner die block 26 b, moves relative tothe other die block 26 a, thereby allowing the pressure imparted by thedrive rollers 18 on the work piece can be maintained substantiallyconstant to maintain drive of the work piece through the processingchannel.

The inner die block 26 b is slidably supported on a plurality of shafts(not shown) which are received through bore holes 28. Although only thelower bore holes 28 are shown in FIG. 1, both upper and lower bore holes28 are provided. FIG. 3 illustrates the configuration of an upper borehole 28. Both the upper and lower bore holes may be staggered relativeto each other or otherwise aligned. The shafts are disposedperpendicular to the first channel section 14 so as to allow theseparation of the die faces 22 a, 22 b to vary relative to each otherwhilst maintaining a generally parallel relationship. The shafts extendbetween the die blocks 26 a, 26 b and through the first channel section14 at a height which will be above and/or below the work piece in use.

It will be appreciated that the shafts may be otherwise fixed relativeto the apparatus so that the shafts don't impinge on the first channelsection 14. In this regard, the inner die block 26 b may be suspendedwithin the apparatus 10 relative to the fixed die block 26 a external tothe first channel section 14.

Movement of the inner die block 26 b along the shaft is restrained bythe action of a resilient spring element (not shown) acting on the dieblock 26 b so that a pressure imparted on the work piece by each dieface remains substantially constant. In this regard, the shaft has ahead at one end thereof. The head of the shaft is configured to bereceived in a correspondingly shaped aperture in bore hole 28. Theresilient spring element is a plurality of spring washers which aredisposed between the head and the die block.

Movement of the inner die block 26 b has been described in relation to aspring loaded system. It will be appreciated that movement of the singledie block 26 b may similarly be performed by other means, such as underthe action of a hydraulic system.

The apparatus 10 further includes a plurality of drive members 18 whichare disposed in the second channel section 16 to pull the work piecethrough the processing channel 12. In the embodiment shown, these arealso in the form of rollers. The drive members 18 are configured so thata combined contact area of the drive members 18 acting on the work piecein the first channel section 14 is substantially equal to a combinedcontact area of the drive members 18 acting on the work piece in thesecond channel section 16. The drive members 18 acting in the secondchannel section to pull the work piece apply a controlled pressure tothe work piece whereby in conjunction with the controlled pressureapplied by the drive members acting in the first channel section controlthe ratio of forces at the entry and exit sides of the apparatus andthereby a controlled tension is applied to the work piece.

FIG. 4 illustrates a roller 30 which is provided to assist in movementof the work piece through the intersection of the first and secondchannel sections 14, 16. The roller 30 is disposed across the secondchannel section 16 from the drive roller 20 and thereby at the innerside of the corner formed by the intersection. The radius of the roller30 is less than half the gauge or thickness of the work piece. It willbe appreciated that if the radius of the roller 30 is too large, theamount of shear deformation performed by the work piece will be reduced.If the radius of the roller is too small, it we be difficult tomanufacture and vulnerable to breakage. A void 32 may be provided behindthe roller 30 for the introduction of lubrication to the work piece. Insuch an arrangement, the roller 30 would drag the lubricant around itssurface and onto the work piece.

In the embodiments shown in FIGS. 1 to 4, the drive members are shown asdrive rollers 18. It will be appreciated that the drive rollers 18 maybe substituted with other drive means such as a belt.

FIG. 5 illustrates another embodiment of the invention. In thisembodiment, the apparatus 110 includes a plurality of clamping elements118 which have a generally planar surface for contacting the work pieceand are disposed around a pair of endless drive members 130 a, 130 b,each of which is in the form of a chain. Each chain 130 a, 130 b passesaround a pair of opposing sprockets 132. Each sprocket 132 is arrangedso that clamping elements 118 which are coupled to a respective chainare in opposing relationship with the clamping elements which arecoupled to the other chain so that a first channel section 114 isdefined between the clamping elements 118. The clamping elements 118engage a work piece 111 as they travel around a straight portion of eachchain 130 a, 130 b so as to drive the work piece 111 through theapparatus 110.

The first and second channel sections 114, 116 are of substantiallyequal cross section and intersect at an angle of 90 degrees to eachother, though it will be appreciated that the first and second channelsections 14, 16 could be arranged at other angles which would preferablybe in the range of 90 to 135 degrees. The second channel section 116extends between an external surface of a drive roller 120 and a diemember 134. As a work piece passes 111 through the apparatus 110 fromthe first channel section 114 to the second channel section 116, it willcontact the drive roller 120 which engages the work piece 111 andadvances it through the intersection. Although the second channelsection 116 is shown as having a curved profile, it will be appreciatedthat the first and second channel sections intersect at an angle of 90degrees and the work piece will be subject to shear deformation throughan angle of 90 degrees.

Disposed adjacent the drive roller 120 are a plurality of idler pulleys136 which are rotatably fixed relative to the drive roller 120. Thespacing between the drive roller 120 and the idler pulleys is such thatas the work piece 111 passes through the second channel section 116, itis compressed between the idler pulleys and the drive roller 120 so thatit is pulled through the second channel section 116. As discussed inconnection with the first embodiment a controlled tension is applied tothe workpiece as it is pulled through the apparatus.

As illustrated in FIG. 8, a surface of the clamping elements 118 whichis arranged to engage the work piece 111 is grooved. The grooves 140 areconfigured to accept corresponding protrusions 142 on a support member144 so that as the clamping elements 118 pass around a curved portion ofthe chain 130 a, 130 b, contact with the work piece 111 passes from theclamping elements 118 to a respective die face in the first channelsection 114.

FIG. 9 illustrates the apparatus 110 with an upper support block 140removed. It can be seen that the protrusions 142 are configured forclose fitting engagement with the grooves 140. Each of the supportmembers 144 is fixed within the apparatus 110 and an outer face of thesupport member 144 forms a part of the first channel section 114.

The separation of the clamping elements 118, and thus the height of thefirst channel section 114, is variable under the action of a hydraulicsystem which includes two hydraulic rams 150. Each ram acts on acoupling member 150 to urge an upper pair of sprockets 132, and in turnthe chain 130 a and the clamping elements 118 coupled thereto, toward alower pair of sprockets, thereby controlling a contact pressure appliedby the clamping elements on the work piece 111. The hydraulic rams 150are configured to apply a relatively constant pressure on the sprocketsso that a relatively constant pressure may be applied to the work piece111 despite variations in thickness. If the height of the first channelsection 114 could not be varied, as the thickness of the work piecevaried pressure upon it would, change and the clamping elements 118 maylose engagement, causing the process to stall.

After the work piece 111 passes through the second channel section 116,the work piece exits the apparatus 110 along conveyors 138 where it maybe coiled or processed through another process.

The apparatus 110 may also include a roller (not shown) at the inside ofthe corner formed by the intersection of the first and second channelsections 114, 116. The roller would be disposed across the secondchannel section 116 from the drive roller 120. Again, the radius of theroller is less than half the gauge or thickness of the work piece. Itwill be appreciated that if the radius of the roller is too large, theamount of shear deformation performed by the work piece will be reduced.A void may be provided behind the roller for the introduction oflubrication to the work piece. In such an arrangement, the roller woulddrag the lubricant around its surface and onto the work piece.

Embodiments of the invention may include means for reducing frictionwithin the apparatus. In this regard, either of apparatuses 10, 110 mayinclude a lubrication system configured to apply lubricant to the workpiece before the work piece passes through the intersection of the firstand second channel sections.

Embodiments of the invention also relate to a method for processingmetals. The method includes driving a work piece to be treated through aprocessing channel which has first and second channel sections whichintersect and are disposed at an angle to each other. The work pieceundergoes shear deformation at the region of intersection between saidfirst and second channels. The work piece is driven through the firstchannel section by engagement of the work piece with a plurality ofdrive members. The method includes varying a separation of the drivemembers in response to thickness variations of the work piece tomaintain drive of the work piece. Advantageously, thickness variationsof the work piece may be accommodated without compromising driveconsistency of the work piece and continuity of the process.

The work piece is driven through an angle of approximately 90 degreeswhen passing through the intersection. The drive members engage the workpiece in both the first and second channel sections and are configuredso that the contact area of engagement in the first channel section issubstantially equal to the contact area of engagement in the secondchannel section.

Because the work piece undergoes shear deformation in one direction, thedescribed method does not provide uniform material properties in thework piece. Accordingly, it is desirable to repeat the process on thematerial by performing shear deformation in an opposite direction toprovide more uniform material properties in the work piece. This may beachieved by arranging two apparatuses in series with each other,however, it will be appreciated that the cost of such an arrangement maybe prohibitive.

In one embodiment, the method includes the step of twisting a leadingedge of the work piece after it exits the second channel and feeding itback into the first channel to form a continuous mobius strip. Theleading edge of the work piece may be welded to a trailing edge of thework piece after twisting so that it is drawn into the apparatus to beprocessed again.

It has been found that if a work piece is processed a plurality oftimes, its material properties continue to increase, though withdiminishing magnitudes. Processing a work piece four times, i.e. twicein each direction, has been found to be a good compromise in terms ofincreased properties and processing time. Accordingly, the method mayinclude the step of passing the mobius strip through the processingchannel four times.

The embodiments have been described by way of example only andmodifications are possible within the scope of the invention disclosed.

1. An apparatus for producing shear deformation in a work piece, theapparatus comprising: a processing channel through which the work piecepasses, the processing channel including first and second channelsections which intersect at an angle to each other; a plurality of drivemembers configured to engage sides of the work piece to drive it throughthe processing channel so that the work piece passes from the firstchannel section to the second channel section to produce sheardeformation in the work piece; and a drive surface disposed at anintersection of the first and second channel sections, the drive surfacebeing configured to engage the work piece and advance it through theintersection, wherein opposing sides of the first channel section aredefined by a pair of die faces relative to which the drive members arerotatably fixed, the separation of the die faces being variable inresponse to thickness variations of the work piece to maintain drive ofthe work piece through the processing channel.
 2. An apparatus forproducing shear deformation in a work piece, the apparatus comprising: aprocessing channel through which the work piece, passes, the processingchannel including first and second channel sections which intersect atan angle to each other; a plurality of drive members configured toengage sides of the work piece to drive it through the processingchannel so that the work piece passes from the first channel section tothe second channel section to produce shear deformation in the workpiece; and a drive surface disposed at an intersection of the first andsecond channel sections, the drive surface being configured to engagethe work piece and advance it through the intersection, wherein opposingsides of the first channel section are defined by a pair of die facesrelative to which the drive members are rotatably fixed, the separationof the die faces being variable in response to thickness variations ofthe work piece so that the pressure imparted by the drive members on thework piece is maintained at a substantially constant level.
 3. Anapparatus according to claim 1, wherein each die face includes aplurality of drive members each separated by a guide plate.
 4. Anapparatus according to claim 1, wherein an external surface of the drivemembers extend into the first channel section to impart pressure on thework piece.
 5. An apparatus according to claim 1, wherein each drivemember is in the form of a roller, an external surface of which formspart of the die face.
 6. An apparatus according to claim 5, wherein therollers of a respective die face are disposed within a die block, anouter surface of which forms the die face.
 7. (canceled)
 8. An apparatusaccording to claim 6, wherein the die block is slidably supported on aplurality of shafts which are disposed perpendicular to the firstchannel section so as to allow the separation of the die faces to vary.9. (canceled)
 10. (canceled)
 11. An apparatus according to claim 6,wherein the die block is movable under the action of a hydraulic system.12. An apparatus according to claim 1, wherein the drive members includea plurality of opposing clamping elements.
 13. An apparatus according toclaim 12, wherein the clamping elements are disposed around a pair ofendless drive members, the clamping elements engaging the work piece asthey travel around a straight portion of each endless drive member. 14.(canceled)
 15. An apparatus according to claim 12, wherein a surface ofthe clamping elements which is arranged to engage the work piece isgrooved, the grooves configured to accept corresponding protrusions on asupport member so that as the clamping elements pass around a curvedportion of an endless drive member, contact with the work piece passesfrom the clamping elements to a respective support member.
 16. Anapparatus according to claim 15, wherein the support member is fixedrelative to the apparatus and an outer face of the support member formsa part of the first channel section.
 17. (canceled)
 18. An apparatusaccording to claim 11, further including a plurality of drive membersdisposed in the second channel section to pull the work piece throughthe processing channel.
 19. An apparatus according to claim 18, whereinthe drive members are configured so that a combined contact area of thedrive members acting on the work piece in the first channel section issubstantially equal to a combined contact area of the drive membersacting on the work piece in the second channel section.
 20. An apparatusaccording to claim 1, wherein the apparatus further includes a roller atan inner corner of the intersection of the first and second channelsections, the roller being disposed across the processing channel fromthe drive surface.
 21. An apparatus according to claim 20, wherein theradius of the roller is less than half the thickness of the work piece.22. (canceled)
 23. (canceled)
 24. A method for processing metals,including driving a work piece to be treated through a processingchannel, the processing channel having first and second channel sectionswhich intersect and are disposed at an angle to each other, the workpiece undergoing shear deformation at the region of intersection betweensaid first and second channels, wherein the work piece is driven throughthe first channel section by engagement of the work piece with aplurality of drive members, the method including varying a separation ofthe drive members in response to thickness variations of the work pieceto maintain drive of the work piece.
 25. A method according to claim 24,wherein the work piece is driven through an angle of approximately 90degrees when passing through the intersection.
 26. A method according toclaim 24, wherein the drive members engage the work piece in both thefirst and second channel sections, the contact area of engagement in thefirst channel section being substantially equal to the contact area ofengagement in the second channel section.
 27. A method according toclaim 24, further including the steps of twisting a leading edge of thework piece after it exits the second channel, fixing it to a trailingedge of the work piece to form a continuous mobius strip and feeding itback into the first channel.
 28. (canceled)